1. Field of the Invention
The present invention relates to high voltage electrical connectors for high voltage cable conductors, and more particularly, to insert plugs and injection plug inserts for insertion in an access cavity of such high voltage electrical connectors.
2. Description of the Related Art
High voltage electrical connectors interconnect sources of energy, such as transformers and circuit breakers, to distribution systems and the like via high voltage cables. These high voltage electrical connectors typically interconnect cables having 15 to 35 kV of electric potential, and are configured such that at least one of the interconnected cables may be easily disconnected from the high voltage electrical connector to create a "break" in the circuit. Because the high voltage electrical connectors may experience corona and other electrical discharges and must be handled by servicemen, they include many safety features to minimize the risk of injury and chance of structural damage to the connector itself and other nearby equipment.
For instance, a conventional high voltage electrical connector or "elbow" connector includes a cable connector assembly within the body of the elbow connector for interconnecting or electrically coupling one cable within the high voltage electrical connector to a mating electrical contact structure of an associated, mating bushing. The mating bushing is, in turn, electrically connected or coupled to a transformer or other electrical apparatus. The cable connector assembly is surrounded by an insulating dielectric material, except for openings providing access to the internal connector assembly. The insulating dielectric material is surrounded by a conductive shield, typically a molded boot-like item. The conductive shield is electrically connected to a ground such that any voltage which may form on the surface of the electrically insulating material or any electrical discharges near the connector are immediately dissipated to ground.
However, experience has shown that it is desirable to have access to the interior of the high voltage electrical connector. For example, it is often desirable to vent gases from the interior of the connector, conduct tests on the interior cable connector assembly, or take measurements from within the connector. Thus, conventional high voltage electrical connectors may include an access hole extending from the outside of the connector and through the insulative material such that the internal cable connector assembly is exposed.
One use of such an access hole is to inject an insulating liquid into the cable extending from the connector to improve the dielectric strength of the insulative material within the cable. This insulating liquid restores the damaged insulation, rejuvenating the connector. The cables connected to the connector typically include a continuous and cylindrical insulative sheath surrounding the high voltage conductive interior of the cable. This insulative sheath is surrounded by a grounded conductive sheath of metallic material wires located on the exterior of the cable, keeping it at ground potential, tying all neutrals together, and providing a return path for any fault current that may flow due to cable failure.
If water or other contaminants enter into and deteriorate the insulative sheath of the cable, the cable may fail. Thus, the insulating liquid is injected into the cable through the access hole to rejuvenate the dielectric strength of the insulative sheath. For instance, the insulative liquid may be injected into the connector and forced along the entire length of the cable. This insulative liquid penetrates the molecular structure of the cable insulation and cures in place. This re-establishes the original dielectric strength of the cable, greatly lessening the potential for cable failure.
Regardless of the reason for requiring access to the interior of the connector, one dramatic potential problem associated with conventional connectors is that arcing or corona discharges may occur when attempting to gain access to the access hole. This especially may occur when one is working with the connector, such as attempting to inject fluids into the electrical connector and attached cable through the access hole.
A conventional high voltage electrical connector includes a projection of insulating material extending from the grounded conductive shield of the connector body. See, e.g., U.S. Pat. Nos. 4,946,393 and 5,082,449. The access hole is formed in this insulating material projection. Because the insulating projection represents a break in the grounded conductive shield, a separate conductive cap of elastomeric material is configured to fit over the insulative projection and abut against the conductive shield of the body such that the integrity of the grounded shield is maintained. An insulating rod is typically attached to the conductive cap such that it extends into the access hole when the cap is in place. That is, the cap includes a cavity located within the cap for receiving a head of the insulating rod in an interference fit manner so that the two items are attached to each other. When the cap is positioned over the insulative projection, the insulating rod fits within the access hole in an interference fit to provide a dielectric seal. Nevertheless, when the cap and the attached rod are removed from the projection, in order to service or perform tests on the electrical connector, the dielectric seal is broken and the insulative projection is exposed such that there is a large break in the grounded conductive shield.
Due to capacitive coupling, it is common for this exposed insulative projection to develop a high electric potential, especially near the base of the projection even though the insulating material may have excellent dielectric characteristics. Thus, when the cap is removed from the insulative projection, the surface of the projection may be floating at a voltage higher than ground. This voltage may cause corona discharges. After the cap and rod have been removed, an injection port may be inserted into the access hole. Corona discharges may problematically occur during this process because the insulative projection is exposed without a ground shield and the dielectric seal has been broken.
The injection port permits a gas or liquid to be injected into or removed from the interior of the connector and/or cable via the hole formed in the injection port. Conventional injection ports are formed from an insulative material and are sized to fit within the access hole to provide a dielectric seal, similar to the injection plug. These conventional injection ports do not include any grounded shield.
Before or after insertion of a conventional injection port into the access hole, a hose or similar item is connected to a hose connector on the injection port so that the desired maintenance, fluid injection, or tests may be initiated. Because the injection port is not covered with a grounded shield, the surface of the insulating projection and the hose connector may have a dangerous electric potential. This potential may cause arcing. Furthermore, the opportunity for a high surface voltage due to capacitive coupling is enhanced because the liquid, gas, or contaminants within the cable that are removed from the electrical connector and/or cable may be good conductors.
Moreover, because the exiting gases and/or liquids may be conductive, electrical arcing may occur directly out of the hole in the injection port, stemming from the high voltage internal components of the connector. Because the injection port has no conductive shield of any sort, dielectric breakdown of the surrounding air may occur, resulting in arcing to the external surface of the electrical connector and/or other external items, causing damage or injury.
Thus, it is apparent that when a conventional conductive cap is on an insulative projection and when the attached insulating rod is properly placed in the access hole, the ground shield and dielectric seal are operable and capacitive coupling to the surface of the insulating material is typically not a problem. However, when the cap and rod are removed, the insulative projection of the connector is exposed and may have a dangerous electric potential. Furthermore, when the cap and rod are replaced with an injection port, the entire surface of the injection port may float at some voltage significantly higher than ground, and a serious risk of electrical discharges exists when attempting to service the electrical connector through the injection port.
The above-described constraints and problems associated with conventional high voltage electric connectors has created a need for a solution.